The present invention relates to a technique for applying an anisotropic conductive film to a semiconductor wafer.
An anisotropic conductive film (hereinafter to be also referred to as xe2x80x9cACFxe2x80x9d) is a film showing anisotropic conductivity, which shows conductivity in the direction penetrating the front and back of the film and insulation property in the direction of expansion of a film plane. Therefore, by inserting ACF between bare semiconductor element (chip) diced from a wafer and an external circuit board and pressing these three members against each other, electrodes formed on a circuit face of the chip and an external circuit board are electrically connected. The external circuit board is exemplified by a chip-packaging substrate, a typical printed circuit board for co-mounting a chip with other devises, and the like. The use of ACF for mounting a chip has been increasing to meet the recent move toward large-scale integration of semiconductor integrated circuits and fine-pitched connecting terminals (e.g., electrode pad).
Conventionally-known ACFs are formed by dispersing conductive microparticles in a film made of an adhesive insulating material. However, this type of ACF poses structure-related problems, including difficulty in fine pitch connection with the connection target and necessity for a convex (bumpy) electrode on a chip.
To solve these problems, JP-A-3-266306 entitled xe2x80x9cANISOTROPIC CONDUCTIVE FILMxe2x80x9d and WO98/07216 entitled xe2x80x9cANISOTROPIC CONDUCTIVE FILM AND METHOD FOR MANUFACTURING SAMExe2x80x9d propose ACF having a different and new structure. This ACF has a structure wherein a number of conductive paths insulated from each other penetrate a film substrate and both ends of each conductive path are exposed on the front and back faces of the film substrate. This structure solves the above-mentioned problems of fine pitch structure and the shape of electrodes on a chip.
The present inventors further studied the connection between a chip and an external circuit board via the above-mentioned ACF, and now found the following problems.
A first problem is that simultaneous junction of a chip, ACF and an external circuit board in the mounting process does not allow large-scale production.
To solve this problem, the present invention proposes earlier junction of ACF with either a chip or an external circuit board.
However, junction of ACF with a chip according to this method still poses a problem in achieving junction of the two at a large scale and at a sufficiently high throughput (amount to be processed in a given time). In particular, junction of ACF with microsized chips having a size of not more than 5 mmxc3x975 mm, among others, not more than 3 mmxc3x973 mm, defies increase in throughput due to the need of fine and precise alignment for adhesion of ACF to each chip.
To solve this problem, the present invention further proposes earlier adhesion of a large sheet of ACF to a semiconductor wafer before dicing into chips, followed by dicing into each chip. By this method, the throughput can be increased sufficiently.
When the present inventors actually adhered an ACF to a semiconductor wafer for junction, however, air voids often remained between the semiconductor wafer and the ACF during superposition, because the both have large areas. The air voids form voids in the junction part. When a thermal cycle is applied thereto, or upon moisture absorption or temperature rise, peeling proceeds and degrades the connection reliability. Even if the aforementioned problem of voids is resolved, a throughput affording a high level of production amount while retaining the quality in terms of connection reliability between them can be secured only when a new method of efficiently joining the both after superposition by heating while applying a contact load according to an appropriate method. Otherwise, a decrease in the throughput due to cracking of a wafer cannot be prevented.
On the other hand, a laminate of a semiconductor wafer and ACF sometimes warps and, in an extreme case, wafer is cracked, during heating for joining these two members or cooling after joining, due to a great difference in the coefficient of linear expansion between them. When, for example, a semiconductor wafer and ACF are joined after heating to allow junction upon sufficient thermal expansion, it warps in the direction of an arrow as shown in FIG. 10, due to greater shrinkage of ACF upon cooling.
It is therefore an object of the present invention to solve the above-mentioned problems and provide a method for efficiently producing an ACF-semiconductor wafer joined product while retaining fine quality.
Another object of the present invention is to solve the above-mentioned problems and provide an ACF-semiconductor wafer joined product as a structure free of warp.
The present invention is characterized by the following.
(1) A method for producing a semiconductor wafer with an anisotropic conductive film, which method comprises the steps of
sandwiching and depressurizably surrounding a laminate of an anisotropic conductive film on a circuit face of a semiconductor wafer, with flexible films or with a flexible film and a rigid plate, in the laminating direction,
depressurizing the surrounded interior, and
joining the semiconductor wafer and the anisotropic conductive film by pressurization of the laminate at least in the laminating direction and heating as is from the outside.
(2) The production method of the above-mentioned (1), wherein the above-mentioned anisotropic conductive film has a structure comprising a plurality of metal conductor wires as conductive paths, which are insulated from each other, and which penetrate a film substrate made of an insulating resin in the thickness direction thereof, and wherein the insulating resin to be used for the film substrate is a material that acquires adhesion property by heating.
(3) The production method of the above-mentioned (2), wherein the conductive path of the above-mentioned anisotropic conductive film has a solder layer on at least one of the both ends thereof.
(4) The production method of the above-mentioned (1), wherein the above-mentioned laminate is sandwiched with flexible films or with a flexible film and a rigid plate in the laminating direction, via a release layer.
(5) The production method of the above-mentioned (4), wherein the release layer has a thickness of 25 xcexcm-250 xcexcm.
(6) The production method of the above-mentioned (1) or (4), wherein the above-mentioned laminate is sandwiched in the laminating direction with a flexible film and a rigid plate, and a cushion layer is inserted between the laminate and the rigid plate.
(7) The production method of the above-mentioned (1), wherein the semiconductor wafer and the anisotropic conductive film are joined by pressurization of the laminate at least in the laminating direction and heating as is from the outside, the external pressurization is released first and then the temperature is lowered.
(8) A semiconductor wafer with an anisotropic conductive film, comprising an anisotropic conductive film joined on a circuit face of the semiconductor wafer, and an inhibiting layer on a rear face of the semiconductor wafer, which layer causes an expansion-shrinkage force due to the aforementioned temperature change by antagonizing an expansion-shrinkage force generated on the aforementioned anisotropic conductive film due to temperature changes such that the entire film is kept from warping.
(9) The semiconductor wafer with an anisotropic conductive film of the above-mentioned (8), wherein the above-mentioned anisotropic conductive film has a structure comprising a plurality of metal conductor wires as conductive paths, which are insulated from each other, and which penetrate a film substrate made of an insulating resin in the thickness direction thereof, and wherein the insulating resin to be used for the film substrate is a material that acquires adhesion property by heating.
(10) The semiconductor wafer with an anisotropic conductive film of the above-mentioned (9), wherein the conductive path of the above-mentioned anisotropic conductive film has a solder layer on at least an outer end of the both ends thereof.
(11) The semiconductor wafer with an anisotropic conductive film of the above-mentioned (8), wherein the above-mentioned inhibiting layer is made from an organic polymer material.
(12) The semiconductor wafer with an anisotropic conductive film of the above-mentioned (8), wherein the above-mentioned anisotropic conductive film has a (xcex11xc3x97E1xc3x97t1)/(xcex12xc3x97E2xc3x97t2) ratio of a product (xcex11xc3x97E1xc3x97t1) of (a coefficient of linear expansion xcex11, an elastic modulus E1 and a thickness t1) of the above-mentioned anisotropic conductive film to a product (xcex12xc3x97E2xc3x97t2) of (a coefficient of linear expansion xcex12, an elastic modulus E2 and a thickness t2) of the above-mentioned inhibiting layer of 0.5-2.0.
(13) The semiconductor wafer with an anisotropic conductive film of the above-mentioned (8), wherein the above-mentioned inhibiting layer comprises a coloring agent.
(14) A method for producing a semiconductor wafer with an anisotropic conductive film of any of the above-mentioned (8)-(13), which method comprises the steps of
superimposing an anisotropic conductive film on a circuit face of a semiconductor wafer,
superimposing an inhibiting layer on a rear face of the semiconductor wafer, which layer causes an expansion-shrinkage force due to the aforementioned temperature change by antagonizing an expansion-shrinkage force generated on the aforementioned anisotropic conductive film due to temperature changes such that the entire film is kept from warping, and
joining these successively or simultaneously with a semiconductor wafer by heating and/or pressurizing such that respective expansion-shrinkage forces antagonize with each other to inhibit warping.
(15) The production method of the above-mentioned (14), which method comprises the steps of
superimposing an anisotropic conductive film on a circuit face of a semiconductor wafer,
superimposing an inhibiting layer on the rear face of the semiconductor wafer,
sandwiching and depressurizably surrounding this with flexible films or with a flexible film and a rigid plate in the laminating direction,
depressurizing the surrounded interior, and
pressurizing the surrounded interior at least in the laminating direction and heating the surrounded interior as is from the outside, to join the semiconductor wafer with the anisotropic conductive film and the semiconductor wafer with the inhibiting layer.
The semiconductor wafer with an anisotropic conductive film is explained by also referring to as a xe2x80x9cwafer with ACFxe2x80x9d in the following.